Plant viral diseases are numerous, and many of them are of the most virulent type. These diseases take a toll measured in the billions of dollars each year. Such viral diseases are particularly hard to control and virtually impossible to cure. One plant virus can attack many different species of plants and be carried by a large number of different vectors (insects, nematodes, fungi, parasitic vascular plants and agricultural tools). Viruses can also be transmitted from one generation to another through the seed, and some viruses are soil borne.
In mammals, interferon is the most rapidly produced defense mechanism against viral infection. One of the activities induced by interferon in mammalian cells is the conversion of ATP to a series of unique 2',5'-oligoadenylates (Pestka, S. [ed] [1981] Methods in Enzymology, Vols. 78 and 79, Academic Press, New York). Similar, but not identical, plant oligonucleotides are induced by AVF (antiviral factor, or plant interferon) in tobacco plants following tobacco mosaic virus (TMV) infection (Devash, Y. et al. [1981] Virology 111: 103-112).
Recently it was reported that the naturally occurring 2',5'-oligoadenylates, as well as the chemically synthesized 2',5'-oligonucleotide analogs, are potent inhibitors of TMV replication at the nanomolar (10.sup.-9 M) level (Devash, Y., Biggs, S., and Sela, I. [1982] Science 216: 1415-1416; Devash, Y. et al. [1984] Jour. Biol. Chem. 259: 3482-3486).